1. Field of the Invention
The present invention relates to a discrimination device, and more specifically relates to a discrimination device which discriminates between two kinds of discrimination objects by utilizing light reflected therefrom or transmitted therethrough. The present invention is suitably applied to, for example, a discrimination device for identifying any of four possible discrimination objects, which are combinations structured by a planographic printing plate and/or a slip sheet.
2. Description of the Related Art
As an example of a conventional discrimination device, a discrimination device for discriminating between a planographic printing plate and a slip sheet, which protects a photosensitive surface of the planographic printing plate, will be described.
Commonly, a slip sheet for protection is closely adhered to an image recording surface of a planographic printing plate, and these are often plurally stacked in a thickness direction to structure a plate sheaf of the planographic printing plates. Hence, in a case of image-recording at the planographic printing plate by an optical exposure device or the like, it is necessary to extract the planographic printing plates and slip sheets from the plate sheaf one at a time and supply the planographic printing plates to the optical exposure device. Regarding material that has been extracted, there are three cases: a state in which a slip sheet is adhered to a planographic printing plate, a planographic printing plate alone, and a slip sheet alone. There is also a state in which nothing has been extracted. Accordingly, it is preferable to be able to reliably discriminate between these four states, with a simple structure.
For example, Japanese Patent Application (JP-A) No. 2001-247254 describes a discrimination device in which a pair of optical sensors is disposed upward of alternately stacked photopolymer plates and slip sheets. A sensing level of one of these optical sensors is set lower than the other optical sensor. Consequently, with light reflected from a photopolymer plate, both the optical sensors are turned on, but with light reflected from a slip sheet, the one optical sensor is turned off. Thus, it is possible to discriminate between the photopolymer plates and the slip sheets.
However, with this discrimination device, it is only possible to easily discriminate whether a material that is disposed at the top of a stack is a photopolymer plate or a slip sheet, and it is not possible to discriminate between the four states mentioned above.